This invention relates generally to a fluid circuit, and more particularly, to a method and apparatus for determining the status of a valve associated with the fluid circuit.
Fluid circuits are used in mobile machines in many different applications, such as to drive hydraulic cylinders for lifting or controlling the blade or bucket of an earth moving machine, or in machines having a hydrostatic drive train that use fluid power to control the motion of the machine. Proper operation of the valves in these fluid circuits is important to achieve the desired operation of the machine. In addition, accurate status monitoring of the valve is important to ensure that if a valve malfunction, or failure occurs, the appropriate action may be taken to ensure further damage to the fluid circuit, or machine itself does not occur. For example, if necessary, the machine may be quickly stopped.
Some systems, such as that disclosed in U.S. Pat. No. 5,322,003 to Winyard, disclose a system that determines a valve failure by comparing an actual valve pressure with an expected fluid pressure. If the valve is operating within the fixed design parameters, then the valve is determined to be operating properly. However, Winyard does not disclose determining an error threshold in response to a circuit characteristic, and using the error threshold when comparing the actual and expected fluid pressures. Therefore, circuit conditions which may effect the operation of the fluid circuit are not accounted for. In addition, changes in the circuit conditions are not accounted for. The result is that the Winyard system may not accurately determine when a failure exists, in part because the system does not account for the conditions of the circuit. Therefore, in one example, false alarms may exists which could inappropriately lead to system shut down or maintenance requests. In addition, the expected valve pressures of the Winyard system are determined offline and downloaded to the system. Therefore, variations in the manufacturing of the fluid circuit hardware may not be accounted for in the comparison of the actual with expected pressure values.
The present invention is directed to overcoming one or more of the problems identified above.
Some systems, such as that disclosed in U.S. Pat. No. 5,322,003 to Winyard, disclose a system that determines a valve failure by comparing an actual valve pressure with an expected fluid pressure. If the valve is operating within the fixed design parameters, then the valve is determined to be operating properly. However, Winyard does not disclose determining an error threshold in response to a circuit characteristic, and using the error threshold when comparing the actual and expected fluid pressures. Therefore, circuit conditions which may effect the operation of the fluid circuit are not accounted for. In addition, changes in the circuit conditions are not accounted for. The result is that the A go Winyard system may not accurately determine when a failure exists, in part because the system does not account for the conditions of the circuit. Therefore, in one example, false alarms may exist which could inappropriately lead to system shut down or maintenance requests. In addition, the expected valve pressures of the Winyard system are determined offline and downloaded to the system. Therefore, variations in the manufacturing of the fluid circuit hardware may not be accounted for in the comparison of the actual with expected pressure values.
In another aspect of the present invention, an apparatus is configured to determine a status of a valve in a fluid circuit is disclosed. The circuit has a pump configured to deliver fluid to the circuit. The apparatus includes a sensor configured to sense a characteristic of the fluid in the fluid circuit and responsively generate a fluid characteristic signal; and a controller configured to receive the fluid characteristic signal, establish an expected value of the fluid characteristic, and determine a valve status in response to the sensed fluid value and the expected value.